The latest incarnation in the Birmingham Development Company portfolio is set to create the United Kingdom’s highest public square and the “Taj Mahal” of car parks.

Speaking for the first time about proposals for the former Birmingham Post & Mail building in Colmore Circus, BDC boss Alan Chatham said the development would be the company’s most ambitious scheme yet.

Birmingham Development Company earned its reputation by transforming the former Royal Mail sorting office into The Mailbox and is currently building out the Ken Shuttleworth-designed Cube, which is set to be completed at the end of next year.

But despite the intricate challenges of The Cube – the mixed-use scheme being developed alongside the canal basin at the back of The Mailbox that will eventually be the new home of the Highways Agency – Mr Chatham said developing the former home of The Birmingham Post threw up a whole set of new challenges.

He said: “One of the unique features of this building is the huge underground area where the former presses were housed and so we are using this to our advantage. We have done something similar at The Cube but on that project, we had to spend millions digging an unbelievably large hole in the ground.”

Mr Chatham would not be drawn into more detail about that element of the plans other than to describe it as the “Taj Mahal” of car parking and an essential income stream for the project.

For him, the headlines will be made by what happens at the top of the development rather than the bottom.

“The key behind this development is to create something in the city’s office district that you can see above all others – something that will stand out in an area of pretty nondescript buildings,” he said. “When we were looking at the possibilities for this building, we looked at it from across the city and you can see it from the ring road, you can see it from Snow Hill station and on the trains as you approach Snow Hill and you can see it coming in on the Aston Expressway. This is a great opportunity to make a real statement.”

The outline plans for the scheme, which have been drawn up by Associated Architects and are set to be submitted to Birmingham City Council for consideration in the coming days, will see a car parking element at the bottom, with offices on top of that and then a huge 50m by 50m ‘window’ at the front and back of the building, inside which will be a public space with restaurants and a separate level of high-specification residential.

“If you look around the office district, there is no real square – not somewhere where people can sit and relax or meet or eat,” said Mr Chatham. ‘‘There is still a good deal to work to be done on the detail of the square but the window would probably have glass for the first five metres – “we don’t want people getting blown off” – and the rest is very much up in the air, so to speak. We don’t believe that residential is dead in the city centre – we think that’s crazy,” he said “We want to create quality residential offer where families want to live, very much in the same vein as the Mailbox, which is seeing an increasing number of families making it home.

“I was just talking to the architect who was suggesting ideas such as telescopes looking out over the city, but it is too early to say how this will finish up. I see the square as somewhere to sit and relax. The thought of making it very arts-based is appealing – I think of something like the area outside the Museum of Modern Art in New York with pieces of art around a practical space. It would be great to do something as ambitious but that’s a dream at the moment.”